Systematic reviews require comprehensive searches of the literature in multiple databases. In order to create a search query that will attempt to capture all articles on a certain topic, it's important to identify the key concepts of your research question and brainstorm all the possible keywords and controlled vocabulary terms for each concept. Be aware that the first search query that you build for a database won't be the last one. It takes time to develop and modify a search, and you'll likely need to modify it for each database you search.
Keywords are words that could appear anywhere in an article abstract. This includes the article title, journal name, authors, abstract, author supplied keywords, subject headings, and more. Brainstorm as many synonyms for a term that you can to capture all the different ways an author may have phrased or spelled out a concept.
Controlled vocabulary terms, also known as subject heading terms, are words and phrases that have been added to an article record that helps describe what the article is about. These terms are defined in the database's thesaurus and are linked to other controlled vocabulary terms in a hierarchical order.
Controlled vocabulary terms are important because while there could be many ways to express a concept in writing using keywords, such as "quality of life". When using controlled vocabulary terms you're able to search for the meaning of the concept--no matter how the concept can be spelled or the variety of ways that it can be phrased.
The table below shows how for each concept we identify, there can be many synonyms, acronyms, and other like-phrases that we can use as possible search terms.
| E-cigarettes | Smoking Cessation | COPD |
|---|---|---|
|
e-cigarette e-cigarettes electronic cigarette electronic cigarettes e-cig e-cigs |
smoking cessation quit smoking quitting smoking stop smoking stopping smoking give up smoking |
COPD chronic obstructive pulmonary disease COAD chronic obstructive airway disease chronic obstructive lung disease chronic airflow obstruction chronic airflow obstructions |
Once you have your concepts and keywords listed, now list the controlled vocabulary terms for each concept. This will change from database to database, as most have their own set of controlled vocabulary terms (i.e., PubMed has different terms than Embase). For a search in PubMed, you'll want to identify medical subject headings (MeSH) for each concept.
| E-cigarettes | Smoking Cessation | COPD | |
|---|---|---|---|
| Keywords |
e-cigarette e-cigarettes electronic cigarette electronic cigarettes e-cig e-cigs |
smoking cessation quit smoking quitting smoking stop smoking stopping smoking give up smoking |
COPD chronic obstructive pulmonary disease COAD chronic obstructive airway disease chronic obstructive lung disease chronic airflow obstruction chronic airflow obstructions |
| MeSH |
Electronic Nicotine Delivery Systems |
Smoking Cessation |
Pulmonary Disease, Chronic Obstructive |
It's a good idea to take your concept table and write up your search query in a word processor first. It makes editing your searches easier than within the database, and you can copy and paste it into the search box. Here's an example of what a simple search query would look like.
(“Electronic Nicotine Delivery Systems”[MeSH] OR “e-cigarette” OR “e-cigarettes” OR “electronic cigarette” OR “electronic cigarettes” OR “e-cig” OR “e-cigs”) AND (“Smoking Cessation”[MeSH] OR “smoking cessation” OR “quit smoking” OR “quitting smoking” OR “stop smoking” OR “stopping smoking” OR “give up smoking”) AND (“Pulmonary Disease, Chronic Obstructive”[MeSH] OR “COPD” OR “chronic obstructive pulmonary disease” OR “COAD” OR “chronic obstructive airway disease” OR “chronic obstructive lung disease” OR “chronic airflow obstruction” OR “chronic airflow obstructions”)
Keep documentation of your search queries, as you will need to report how the searches were done in the methods section of the paper. Thorough systematic reviews also include the complete search queries in the appendix, so that the searches can be reproduced by others. Document the following information for each database search:
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